Field of The Invention
The present invention relates to the apparatus used for determining the gyroscopic stability of spinning projectiles in which 3 degree of freedom measurements are made of forces and movements. Projectiles usually require high spin rates to obtain the required gyroscopic stability in flight. This motion of a spinning projectile can at present time only be successfully determined by actual projectile firings from a gun. However, this method does not permit closely controlled experiments, nor does it provide for precision measurements over any degree of the range of performance.
Forced motion flight simulators can operate on a projectile so that it is spun and driven in pitch and yaw directions. The spin rates achievable with such a device, however, are much less than those possible with an actual full service spin rate of up to 9,000 revolutions per minute.
Some experiments have been performed using a 3 degree, forced mode fixture to develop and measure forces and moments. The use of ball-bearing races introduce frictional variations which result in significant errors.
Recently, a new development has been attempted in which a spinning projectile was supported by a large spherical air bearing, with 3 degrees of angular freedom, which is positioned externally to the projectile. The geometric center of the bearing is at the combined center of mass of the projectile and the male part of the bearing. This fixture was impractical, however, because projectiles require high spin rates to obtain the required gyroscopic stability in flight. Therefore the tangential velocity differencial between the male and female parts of the support bearing, particularly for large projectiles, became overwhelming. The diameter of the spherical air bearing must be at least twice that of the projectiles it supports so as to prevent unrealistic limitations to the projectile yawing motion during spin down.
Accordingly, it has not been possible to operate on large caliber projectiles of from less than 75 mm to greater than 120 mm which operate at full service spin rates of up to 9,000 revolutions per minute. It is necesary during this high full service spin rate to provide for large amplitude pitching of up to 15 degrees and yawing motion at a service rate of up to 15 Hertz. The tangential velocity of the spherical air bearing does not permit anywhere near the approximation of these values.
Accordingly, it would be a great advantage to the art if a device could be provided which would permit the development of and measurement of gyroscopic stability effects in spinning projectiles and the interaction between projectiles and their pay loads. It is particularly desireable that the device be capable of operating at speeds up to 9,000 RPM for full size artillery projects up to and exceeding the 155 mm artillery projectile. It is particularly desireable that a simulation device be provided so that the motion of the projectile is natural and not forced, so that the interaction between the projectile and the driving system would not be too severe to permit accurate measurements of projectiles weighing upwards of 100 lbs.